A wide variety of refrigeratable bread doughs are sold commercially. These doughs most commonly utilize chemical leavening agents, which generally comprise a combination of a leavening acid (e.g., citric acid, phosphate salts or glucono delta lactone (GDL)) base (e.g., bicarbonate of soda). These acidic and basic components react with one another to generate carbon dioxide to "proof" the dough. In this proofing process, the chemical leavening agent generates a sufficient quantity of carbon dioxide to cause the dough to rise within the container. By using known quantities of the components of the leavening agent, the total volume of carbon dioxide generated can be carefully controlled.
It is widely recognized that yeast-leavened doughs are superior to chemically leavened doughs, though. In particular, yeast-leavened doughs generally exhibit better taste, aroma and texture than do chemically leavened doughs. The yeast and the by-products its fermentation in the proofing or leavening process tend to give the dough a more "home-baked" flavor and aroma than commercially produced doughs using chemical leavening agents.
Yeast is often used in producing frozen bread doughs. In commercially manufacturing these doughs, a large batch of dough is generally made and divided into smaller portions, which may be individually packaged and frozen for ultimate sale to consumers. Freezing the dough halts the fermentation activity of the yeast, preventing the yeast from leavening the dough. When the consumer desires to bake the frozen bread dough, the bread dough is thawed and must be allowed to stand at room temperature so the yeast may leaven the dough before the dough may be baked. Although such frozen bread doughs may produce a superior final baked product, the additional time and inconvenience required by yeast-leavened refrigerated bread doughs limit their appeal to consumers.
Attempts have been made to utilize yeast in leavening a refrigeratable dough. However, yeast is problematic in these types of doughs in that its leavening action is not readily controlled. Whereas the total volume of carbon dioxide generated by chemical leavening agents can be very accurately and reproducibly controlled by controlling the quantity of the leavening agent in the dough composition, such control is not found with yeast strains known in the art. This is primarily due to the fact that yeast is a living organism and will continue to generate carbon dioxide at refrigeration temperatures.
Commercially produced refrigeratable doughs are sold in substantially air-tight containers. The carbon dioxide generated during the proofing process generally builds pressure within the container of about 15-20 psi. If the pressure within these containers substantially exceeds that pressure, the containers will rupture. Accordingly, yeast-leavened doughs cannot be sold in these containers because their shelf life would much too short for an acceptable commercial product--these packaged doughs would explode well before the end of current doughs' shelf life. Furthermore, even if one were to package the yeast in a much more expensive container, such as a hermetically sealed metal can, when the consumer opens the can the sudden release of substantial internal pressure could damage the dough or create other problems.
A number of attempts have been made to adjust the formulation of a yeast-leavened dough to limit the fermentation activity of the yeast. For instance in U.S. patent application Ser. No. 732,081 (filed Jul. 18, 1991), now abandoned, which is owned by the assignee of the present invention and incorporated herein by reference, the yeast used in the dough composition is adapted to substantially cease fermentation at refrigeration temperatures.
Yeast proofs dough better in aerobic atmospheres than it does in anaerobic atmospheres. Nonetheless, yeast will continue to proof dough under anaerobic conditions, albeit generally at a lower rate. In commercially packaging doughs, a head space generally must be left within the container so that the doughs will have room to rise within the container during the manufacturing and packaging process. The head space generally comprises air and the yeast will tend to consume the oxygen in that air relatively rapidly. However, when the oxygen within the head space has been consumed by the dough, the yeast simply starts to ferment under anaerobic conditions and continues to generate carbon dioxide. As explained above, the continuing build-up of carbon dioxide will eventually cause the container to rupture.
Another problem encountered with refrigeratable bread doughs is that they tend to "gray" in the presence of oxygen. When oxygen comes into contact with the dough during refrigeration, it will tend to oxidize certain components in the outermost layers of the dough. These reactions cause the outer skin of the dough to turn a rather unappealing gray color, which consumers generally find unacceptable. Thus, commercially-produced refrigeratable bread doughs must be packaged in substantially gas-impermeable containers to prevent the dough from coming into contact with oxygen. As noted above, such containers would prevent the use of yeast to leaven the dough because the containers would tend to rupture.
Substantial research and development has gone into attempts to provide a commercially salable yeast-leavened dough which may be refrigerated for extended periods of time. Despite all of this concerted effort in the industry, though, there are no commercially-produced doughs which are leavened with yeast yet may be stored for extended periods of time at refrigeration temperatures.